Cheng-Yong Su
Cheng-Yong Su, Sun Yat-sen University, China
Title: Regioselective and enantioselective photoredox catalysis within self-active coordination space of a homochiral Ru(II)-metalloligand-based Pd(II) nanocages
Biography
Biography: Cheng-Yong Su
Abstract
Regio- and enantioselective photodimerization of naphthols and derivatives is attained within a chiral Ru(II)-metalloligand-based palladium(II) nanocage for the first time. The chiral octahedral Ru(II) catalytic centers on the ΔΔΔΔΔΔΔΔ-/ΛΛΛΛΛΛΛΛ-cage walls convert naphthol derivatives into the exclusive S-/R-napthoquinone products with much higher chiral induction in comparison to the chiral RuL3 catalysts in bulk solution. The enhanced stereoselectivity is rationalized by the interplay of confined-space effect and aryl-aryl interactions between host and guest, which could stereo-control the transition state structures. The reaction mechanism has been investigated by Electron Spin Resonance (ESR) spectra, Cyclic Voltammetry (CV), UV/Vis absorption and fluorescence spectra. The results support the fact that the Ru(II) cage undergoes photoexcitation and subsequent oxidation by O2 to give OH radicals and a Ru(III) intermediate cage. The Ru(III) intermediate is then capable of oxidizing naphthol substrate and removing an electron to provide the arene radical species, which is coupled with OH radical to give the naphthalene-1,2-dione intermediate, followed by rearomatization with the arene radical, and then form a C-C bond to obtain the napthoquinone product without any significant observable byproduct. This dimerization reaction constitutes a very rare example of high asymmetric induction in oxidative biaryl coupling from a chiral photocatalyst, which closely resembles to biological systems.